Concerning the choice of an antibiotic regimen with a high chance of effectively eradicating ESBL-E from the gut, data from previous studies has been taken into account. Most previous study concepts were based on the idea of SDD.14-16 SDD aims to eradicate abnormal aerobic gram-negative bacteria, while preserving anaerobic bacteria. In this setting, the problem of adverse events caused by systemic effects of the antibiotics used can be discarded. However, if only locally active antibiotics are used for achieving eradication, patients are less likely to clear concurrent ESBL-E colonization of the throat, skin and urinary bladder. These body sites may then serve as a source of intestinal re-colonization with ESBL-E. Therefore, the current pilot study uses a combination of a non-absorbable enterally administered antibiotic and a systemic antibiotic. To facilitate the choice of an optimum non-absorbable antibiotic, antimicrobial susceptibility testing of clinical isolates of ESBL-E from haematological high-risk patients was carried out at the University Hospital Cologne in 2012. Virtually no resistance towards colistin could be detected (data not published), such that colistin was chosen as the non-absorbable component. As previous studies have shown promising results for a combination of colistin and gentamicin, the latter was added to the eradication regimen. Concerning the choice of a systemically active antibiotic, promising data on the clinical efficacy of fosfomycin in ESBL-E infections and in the reduction of ESBL-E in the intestinal flora have been published. Given the additional convenience of an available oral formulation - a prerequisite not given for most other ESBL-E active treatments - fosfomycin was chosen for combination with oral colistin and gentamicin. For the treatment of urinary tract infections, oral fosfomycin is usually administered as a single dose of 3g. However, several studies have assessed treatment of complicated or chronic urinary tract infections with repetitive administrations of 3g fosfomycin.